1. Field of the Invention
This invention relates to storage devices for storing semi-conductor wafer cassettes known as stockers and more particularly relates to a modular stocker that simplifies repair and maintenance by removal and replacement of system modules.
2. Background Information
Semi-conductor wafer fabrication involves hundreds of processes for producing electronic chips or integrated circuits such as microprocessors, computer memory and other microcircuits. Throughout the fabrication process, the semi-conductor wafers are transported from one processing station or area in sealed cassettes. The cassettes separate the wafers and prevent wafer-to-wafer contact. The cassettes are transported in sealed containers or in plastic boxes or may be open without container. The semi-conductor wafers must be kept in a class 1 substantially contaminant-free environment throughout the fabrication processing.
In between processing steps the cassettes for the semi-conductor wafers are stored in enclosures known as stockers. Each cassette may have up to twenty-five 200 mm (8 inch) semi-conductor wafers. The cassettes are manually or by an automatic transport system moved out of the stockers through a port or window to a processing station. After each process is complete, the semi-conductor wafers are returned to the cassette and then usually delivered back to the stocker to await further processing or to another stocker at the next processing step. There may be very many stockers strategically placed at intervals along the production line for easy access by personnel performing the processing.
The stockers have a plurality of open frame slots or shelves inside a substantially rectangular or half cylindrical enclosure. Semi-conductor wafer cassettes are returned or retrieved through a port or window in the stocker. After a particular process is complete, the semi-conductor wafer cassette is either manually or by an automatic transport system returned to a shelf at the in/out window or port. An automatic pick up and transfer device picks up the semi-conductor wafer cassette and places it in an empty slot or shelf in the stocker to await the next processing step.
The pick up and transfer device is comprised of a horizontal linear-arm that is moved up and down inside the stocker, has a paddle or gripper for picking up the cassette or cassette container and is driven by several programmed servo motors. Vertical and rotational movement of the linear arm is performed by the programmed servo motors. Another servo motor moves the paddle or gripper horizontally in and out into position beneath a cassette. The system always knows where there is an empty slot or shelf in the stocker. Once a semi-conductor wafer cassette is placed in the input port, the pick up and transfer device is triggered to move into position vertically and rotationally at the input port, moves the paddle forward to pick up the cassette. The paddle with the cassette is then retracted and the pick up and transfer device quickly moves inside the stocker to a position adjacent an empty slot or shelf. The paddle then deposits the cassette on the shelf and is retracted and the linear arm returned to a standby position to await the next semi-conductor wafer cassette being retrieved or stored. The retrieval of a semi-conductor wafer cassette from the stocker is just a reversal of the process of storing a cassette described above.
Since there are very many of these stockers throughout the processing plant, it is essential that they be kept operational as much as possible. Breakdowns in the stocker electronic circuits or pick up and transfer device can disrupt the entire production line causing costly delays. Stockers currently available have to be dismantled to get at electronic circuits and pick up and transfer devices when there is a breakdown. The breakdowns cause downtimes of at least many hours, or days and can be even longer.
It is therefore one object of the present invention to restore a semi-conductor wafer cassette stocker to service in the shortest possible time.
Another object of the present invention is to provide a semi-conductor wafer cassette stocker that can be returned to service in minutes rather than hours or more.
Still another object of the present invention is to construct a stocker with modular assemblies that can be easily and quickly replaced.
Yet another object of the present invention is to provide a semi-conductor wafer stocker with modular electronic circuits mounted on roll-in roll-out panels that can be easily and quickly removed and replaced.
Still another object of the present invention is to provide a pick up and transfer device on a removable chassis that can be quickly and easily detached from the stocker and replaced. Yet another object of the present invention is to mount the pick up and transfer device chassis on casters to allow it to be detached quickly and removed from the stocker frame.
The purpose of the present invention is to provide an improved semi-conductor wafer cassette stocker that simplifies maintenance to minimize down time when repairs or replacements are required.
The stocker of the present invention is comprised of a rectangular or square frame formed of a plurality of vertical beams joined by horizontal extending joists. The outer surface of the stocker frame is covered with a skin of sheet metal or plastic bolted or otherwise secured to the stocker frame to form an enclosure. One, two or three sides are provided with port(s) or window(s) with a shelf at a comfortable height to place semi-conductor wafer cassettes on the return or retrieval from the stocker. A plurality of wire shelves are positioned and attached in rows and columns inside the stocker frame. The stockers may vary in overall size-which depends upon the space available in the production plant. They can be sufficient length, width, and height to store twenty or more semi-conductor wafer cassettes or cassette containers.
Access to and retrieval of the semi-conductor wafer cassettes is by a pick up and transfer system comprised of a rotatable linear arm mounted on a rotary pedestal or platform that is attached to a belt driven linear actuator by a servo motor for precise vertical positioning. A second servo motor rotates the linear arm through an approximately 180 degree range to provide access to semi-conductor wafer cassettes stored on three to six vertical columns within the stocker. A third servo motor moves a pick-up paddle forward and backward to advance, lift, and retract a semi-conductor wafer cassette or cassette container.
The entire pick up and transfer mechanism is mounted on a chassis forming a unitary removable drive assembly. This drive assembly forms one side of the stocker enclosure. The lower end of the assembly has a base or pedestal supporting the linear arm, paddle, and all servo motors. A central vertical beam houses a belt driven vertical linear actuator and is attached to and extends vertically the full height of the stocker.
The drive assembly is uniquely constructed to be removable as a unit from the stocker for repair or replacement. The chassis of the drive assembly has cross braces with quick disconnect fasteners. The cross braces extend horizontally across one side at the top and bottom of rectangular frame of the stocker. Each end of the cross braces fit onto a bolt that is grasped by a quick connect fastener. Rotation of the quick connect fastener in one direction disconnects each end of the upper and lower cross braces allowing complete removal of the drive assembly.
Casters or rollers at the bottom on each corner of the chassis allow the entire assembly to be simply rolled out of the stocker once quick disconnect fastener has been released. This allows removal and replacement of the entire drive assembly in minutes substantially reducing present down times of many hours or days needed to disassemble parts of the stocker to make repairs or replacements.
An additional unique feature is the mounting of all system electronics on removable boards or panels. The electronics are preferably mounted in the stocker on boards or panels that have channels along opposite sides that engage rails on the interior sides of the stocker. Two removable electric panels mounted at the lower end on either side of the drive assembly are preferred. The electronic circuits are connected to the drive system by standard plugs that engage a battery of sockets mounted on the drive assembly chassis or on the electronics panels themselves.
The electronic circuit panel assemblies are removable from the drive assembly side or the opposite side of the stocker frame. They are removed by disconnecting the plugs, and then rolling the entire panel off the rails.
This construction allows all electronic circuits and the drive assembly to be removed and replaced in minutes substantially reducing down time and interruption of the production line. The pick up and transfer drive assembly can be disconnected electronically and mechanically and simply rolled out of the stocker. A replacement drive assembly can be rolled in the plugs reconnected and the quick disconnected fasteners engaged restoring service in minutes. Likewise, the circuit panels can be rolled off the rails and replaced quickly.
The above and other objects, advantages, and novel features of the invention will be more fully understood from the following detailed description and the accompanying drawings, in which: